SegmenTree.java

anwarshaikh078 · abranhe · commit d300f1de8f7b · 2020-10-06T16:36:00.000-04:00
I have created a Segment tree, to find maximum element in given range.
diff --git a/SegmentTree.java b/SegmentTree.java
@@ -0,0 +1,101 @@
+import java.util.*;
+import java.lang.*;
+import java.io.*;
+class SegmentTree
+{
+    int st[];
+    Segment(int []arr, int n)
+    {
+        int x = (int) Math.ceil((Math.log(n)/Math.log(2)));
+        int max_size = 2 *(int) (Math.pow(2,x) - 1);
+        st = new int[max_size];
+        
+        constSegmentUtil(arr,0,n-1,0);
+    }
+    
+    int constSegmentUtil(int []arr, int ss,int se,int si)
+    {
+        if(ss == se)
+        {
+          st[si] = arr[ss];
+          return arr[ss];
+        }
+        int mid = getMid(ss,se);
+        st[si] = max(constSegmentUtil(arr,ss,mid,2*si+1),constSegmentUtil(arr,mid+1,se,2*si+2));
+        return st[si];
+    }
+    
+    int getMid(int s,int e)
+    {
+		  return s + (e - s)/2;
+    }
+    
+    int max(int a,int b)
+    {
+      if(a > b)
+      {
+        return a;
+      }
+      else{
+        return b;
+      }
+    }
+    
+    void print(){
+        for (int i=0;i<st.length;i++ )
+        {
+            System.out.print(st[i]);
+        }
+    }
+    
+    int getMaxUtil(int ss,int se,int qs,int qe,int si)
+    {
+        if(qs<=ss && qe>=se)
+        {
+            return st[si];
+        }
+        
+        if(se<qs || ss>qe)
+        {
+            return 0;
+        }
+        
+        int mid = getMid(ss,se);
+        
+        return max(getMaxUtil(ss,mid,qs,qe,2*si+1),getMaxUtil(mid+1,se,qs,qe,2*si+2));
+    }
+    
+    
+    int getMax(int n,int qs,int qe){
+        
+        if(qs > qe || qs < 0 || qe > n-1){
+            return -1;
+        }
+        
+        return getMaxUtil(0,n-1,qs,qe,0);
+    }
+    
+	public static void main (String[] args) throws java.lang.Exception
+	{
+		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+		int t = Integer.parseInt(br.readLine());//for testcase
+		String []temp = br.readLine().split(" ");//taking array as string
+		int []arr = new int[t];
+		for(int i=0;i<t;i++) //to convert array of string to array of integers
+		{
+		    arr[i] = Integer.parseInt(temp[i]); 
+		}
+		Segment tree = new Segment(arr,arr.length);
+		//tree.print();
+		int q = Integer.parseInt(br.readLine()); // no of queries
+		while (q--!=0)
+		{
+		    String []temp1 = br.readLine().split(" ");
+		    int s = Integer.parseInt(temp1[0]); //q1
+		    int e = Integer.parseInt(temp1[1]); //q2
+		 
+		    System.out.println(tree.getMax(arr.length,s-1,e-1));   // maximum in range [q1,q2]
+		    //System.out.println(getMax(arr,n,s,e));
+		}
+	}
+}
